1. Field of the Invention
This invention generally relates to an apparatus for applying electrical stimulation to reduce pain. In particular, it relates to a stimulation system that can be worn by a patient to reduce pain at joints or other flexing body portions caused by such conditions as carpal tunnel syndrome.
2. Description of the Prior Art
Carpal tunnel syndrome (CTS) is a common and troublesome condition that interferes with the use of the hand. CTS is caused when too much pressure is put on a nerve that runs through a person's wrist. Symptoms of CTS include progressive pain and numbness in the hand. These symptoms occur because the median nerve is compressed as it passes through a narrow tunnel of bone (i.e., carpal tunnel) and ligament at the wrist. The carpal tunnel nerves can be damaged by repetitive motions such as typing or hammering. Nationally, carpal tunnel syndrome annually affects 230,000 workers, costing approximately $3,500 in benefits and rehabilitation per patient.
Neuromuscular stimulation (NMS), transcutaneous electrical nerve stimulation (TENS), and interferential stimulation are three types of electrical stimulation utilized to relieve pain or reduce edema. NMS and TENS, which are the conventional methods of providing electrical stimulation at the surface of the skin, deliver most stimulation to the skin surface directly under an electrode. Adequate pain relief may require careful placement of multiple skin surface electrodes. Moreover, where the pain source is significantly separated from the skin surface, the stimulation (or sufficient stimulation) may not reach the affected area.
Usually, stimulation from NMS and TENS unit is provided via sponge or conductive rubber or elastomeric adhesive electrodes placed at specific locations on the skin. But other approaches have been proposed. U.S. Pat. No. 4,664,118 discloses a glove 10 with a layer of woven metal mesh material to serve as one electrode in an apparatus that provides TENS signals to treat a hand. In this apparatus the entire hand area to be treated is enveloped with the electrically conductive mesh. When the glove acts as one electrode, then a second electrode, such as a metal pad, is required on the patients arm to be able to stimulate the painful hand.
Other delivery methods for the treatment of painful areas with electric stimulation are also known. U.S. Pat. No. 5,067,478 discloses an electrode glove with a layer of conductive material on the shell of the glove. A TENS unit is connected to the electrode glove via a connector. The gloves are used in pairs to deliver electro-massage or electro-acupuncture. A conductive lotion, gel, or warm water is applied to the area of the patient to be treated, and the gloves are placed fiat on that area.
In contrast to TENS and NMS methods, interferential stimulation can concentrate the stimulation deep in the affected tissue. Interferential stimulation uses the constructive and destructive interferences of two slightly different frequencies to produce a beat frequency (see FIG. 12) at locations where both frequencies are present. This interference between the two differing frequencies allows an area to be treated by the stimulation that is typically not effectively reachable with NMS and TENS techniques. U.S. Pat. Nos. 3,895,639 and 4,909,255 both show apparatus that apply interferential stimulation.
Interferential electrical stimulation treatment has been used to relieve the pain experienced by people suffering from carpal tunnel syndrome. Currently, to apply interferential stimulation, a patient is required to place skin electrodes on his hand/arm. The patient is directed to place the four skin electrodes in a criss-cross pattern. The first skin electrode must be placed on the interior side of the wrist. The second skin electrode must be placed on the exterior side of the wrist. The third skin electrode is placed on the back side of the hand and the fourth skin electrode must be placed on the palm at the base of the third metacarpal. Once the skin electrodes are in place, the patient must then correctly connect four wires, one connecting each skin electrode to the stimulation unit. After the patient has managed to place and connect the electrodes correctly, the patient is restricted in movements, because movement of the hand may cause the wires to disconnect or tangle or catch on objects or cause the skin electrodes to fall off the patient's hand/arm. Consequently, this treatment as currently applied is so complex and cumbersome that many patients have difficulty or do not follow their prescribed treatment.
The prior art does not disclose a simple apparatus to allow a patient to apply electric stimulation to the area of carpal tunnel pain. Moreover, the known apparatuses in the prior art make it difficult for a patient to use his/her hands and restrict the ease with which the patient can move about during treatment.